A wireless local area network (WLAN) typically includes an Access Point (AP) and one or more stations. APs and stations transmit data in units referred to as frames over a shared-communications channel. Frames transmitted from a station to an AP are referred to as uplink frames, and frames transmitted from an AP to a station are referred to as downlink frames. In a situation where two or more stations (or an AP and a station) transmit frames simultaneously, then one or more of the frames can become corrupted, referred to as a collision. As a result, Wireless Local Area Networks (WLANs) typically employ one or more protocols to ensure that a station or AP can gain exclusive access to the shared-communications channel for a predetermined interval of time in order to transmit its frames without collisions occurring. Certain wireless network protocols (e.g., Institute of Electrical and Electronics Engineers [IEEE] 802.11, etc.) provide for the AP to periodically broadcast a special frame called a beacon that can be heard by the stations in the BSA (basic service area), the area covered by the AP. The beacon contains a variety of information that enables the stations to establish and maintain communications in an orderly fashion, such as a timestamp, which enables stations to synchronize their local clocks, and signaling information (e.g., channel number, frequency hopping pattern, dwell time, etc.).
A station can prolong its battery life by powering off its radio when not transmitting or receiving. When a station powers off its radio, the station is said to enter the “doze” state or “sleep mode”. A station wakes up from the doze state by powering on its radio to enter the “awake” state. While a station is in the doze state, it cannot transmit or receive signals, and is said to be asleep. A station that saves battery life by alternating between alert states and doze states is said to be in power save (PS) mode, and a station that employs PS mode is said to be a power saving station. While a station is asleep, the AP buffers any downlink frames for the station for eventual delivery when station is in the awake state.
One method for receiving buffered frames is described in the IEEE 802.11—1999 standard, and is referred to herein as the “legacy” power save method. In this method, an AP periodically includes a Traffic Indication Map (TIM) in the beacon to identify which stations in power-save mode have downlink frames waiting in the AP's buffer for transmission.
In accordance with legacy power save method, stations in the doze state wake up to receive beacons and check the TIM. If the TIM indicates that there are frames buffered for the station, the station will send a PS Poll to request delivery of a buffered frame. To use PS polls, a station listens to the TIM in a beacon to determine if the AP has buffered frames for the station. When there are buffered frames for the station at the AP, the station sends a PS Poll to the AP signaling to the AP that the station is awake and waiting to receive a buffered frame. The AP sends a buffered frame to the station. If the frame has the “More Data” bit set to 1, indicating that there are more buffered frames for the station, the station will send another PS Poll to get another buffered frame. This is repeated until the AP has no more frames for the station.
Another strategy for delivering buffered packets in the AP to the appropriate station is known as Automatic Power Save Delivery (APSD), wherein the delivery of downlink buffered frames occurs without the need for PS Polls to indicate that the PS station is awake and ready to receive transmitted frames. There are two types of APSD: (i) scheduled APSD and (ii) unscheduled APSD. The two APSD variants differ with respect to initiation of the ‘service period’, which is the time period during which the PS station is presumed awake and able to receive a frame transmitted by the AP. With scheduled APSD, the service period starts automatically—that is, without special signaling frames to notify the AP that a station is awake and ready to receive frames. With unscheduled APSD, the transmission of an uplink frame is sufficient to signal the start of the service period, i.e., that the station is awake and ready to receive transmitted frames. The unscheduled service period begins when the AP receives from the station a QoS Data/Null frame. The station may elect to limit the access category (AC) of the frame that may initiate a service period. The AC(s) of the frames that may initiate a service period are designated by the station to through signaling such as an APSD TSPEC
Another feature of APSD relates to the termination of the service period, the time interval a PS station must remain awake. Unlike legacy power save, where a PS station may go to sleep after receiving a single frame from the AP, APSD requires a PS station to stay awake to receive several buffered frames, and go to back to sleep only when it is notified by the AP. The AP sets the EOSP (end of service period) bit to 1 in the last frame it transmits in order to signal to the station that it will not transmit any more frames downlink until the next service period. This signals the station that it can go back to sleep.
A mesh network is a network that employs one of two connection arrangements, full mesh topology or partial mesh topology. In the full mesh topology, each node is connected directly to each of the others. In the partial mesh topology, nodes are connected to only some, not all, of the other nodes. A mesh network may contain Mesh Points, Mesh Access Points (MAPs) and portals, collectively referred to as nodes. A portal is a gateway which provides an infrastructure mesh network access to a Distribution System (DS).
The ability to select the different physical channels to be used by the radios at the mesh points (MPs) as the channels become available simplifies channel assignment and/or increases throughput in a mesh. Channels become available when transmissions at nearby MPs complete. A MP can select a channel that is free at the time of arrival of new frames. A channel's idle/busy status can be tracked by each MP through the exchange of control frames that reserve time on different channels. The reservation control frames are exchanged between MPs on control radio(s). Each of the control radios is assigned a fixed physical channel, as communication with neighbor mesh points must remain constant in order to receive reservation messages, which arrive unscheduled. Traffic is carried on mesh traffic (MT) radios. If a MP does not have enough radios to accommodate mesh traffic, control radios may also carry mesh traffic, in addition to control traffic. Mesh traffic radios carry only mesh traffic (no control traffic). The physical channels assigned to mesh radios may change dynamically